Bradford A. Hawkins

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It is often claimed that we do not understand the forces driving the global diversity gradient. However, an extensive literature suggests that contemporary climate constrains terrestrial taxonomic richness over broad geographic extents. Here, we review the empirical literature to examine the nature and form of the relationship between climate and richness.(More)
The diversity of life is ultimately generated by evolution, and much attention has focused on the rapid evolution of ecological traits. Yet, the tendency for many ecological traits to instead remain similar over time [niche conservatism (NC)] has many consequences for the fundamental patterns and processes studied in ecology and conservation biology. Here,(More)
David J. Currie,* Gary G. Mittelbach, Howard V. Cornell, Richard Field, Jean-Francois Guégan, Bradford A. Hawkins, Dawn M. Kaufman, Jeremy T. Kerr, Thierry Oberdorff, Eileen O’Brien and J. R. G. Turner Abstract Broad-scale variation in taxonomic richness is strongly correlated with climate. Many mechanisms have been hypothesized to explain these patterns;(More)
Herbivore species newly introduced into foreign locations (hosts as invaders) are often attacked by native parasitoid species. Here we compare the structure and diversity of 87 such parasitoid complexes with those on the same herbivore species in their native regions (hosts as natives). Overall parasitoid attack rates are generally lower on hosts as(More)
School of Geography, University of Nottingham, University Park, Nottingham, UK, Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA, Department of Environmental Science and Policy, University of California, Davis, CA, USA, Department of Biology, University of Ottawa, Ottawa, ON, Canada, Departamento de Biologia Geral,(More)
We tested the proposition that there are more species in the tropics because basal clades adapted to warm paleoclimates have been lost in regions now experiencing cool climates. Molecular phylogenies were used to classify species as "basal" and "derived" based on their family, and their richness patterns were contrasted. Path models also evaluated(More)
It is widely believed that the diversity of plants influences the diversity of animals, and this should be particularly true of herbivores. We examine this supposition at a moderate spatial extent by comparing the richness patterns of the 217 butterfly species resident in California to those of plants, including all 5,902 vascular plant species and the 552(More)
The observation that ‘‘on the whole. . . larger species live farther north and the smaller ones farther south’’ was first published by Carl Bergmann in 1847. However, why animal body mass might show such spatial variation, and indeed whether it is a general feature of animal assemblages, is currently unclear. We discuss reasons for this uncertainty, and use(More)
Literature data were collected on the floristic distribution and toxicity of phytochemicals to herbivores and on herbivore specialization in order to test phytochemical coevolution theory. The theory makes four predictions that can be tested with this information. Herbivores can adapt to novel, more toxic chemicals by becoming specialists, or they can(More)
The latitudinal diversity gradient is one of the most important problems in ecology and biogeography, but there is little consensus on its causes. Broad-scale species richness gradients are usually correlated with contemporary climate, with the highest number of species in warm, wet areas (Wright et al., 1993; Hawkins et al., 2003a). Even so, such(More)